Method for continuous cleaning of process water in waste paper treatment with control of the content of inorganic solids

Abstract

The present invention relates to a method and to a device for continuous cleaning of process water circulating in a device for treating waste paper. The process water is supplied, from a unit of the device, to an anaerobic reactor comprising a gas separator, and the cleaned process water is returned back to a unit of the device, wherein this unit is selected from: a pulper; screening device; dewatering unit; oxidation/reduction unit; centrifugal screening device; fine screening device; paper-machine mould section; paper-machine press section; reject treatment unit; fibre recovery unit; and drying section; wherein the content of inorganic solids in the reactor is measured and, if this content exceeds a pre-set limit value, process water from the reactor is continuously fed to a solid-liquid separator for separation into a fraction that is depleted of inorganic solids and a fraction that is enriched with inorganic solids, wherein the fraction that is depleted of inorganic solids is returned to the anaerobic reactor and the fraction that is enriched with inorganic solids is conveyed away out of the device, until the content of inorganic solids in the process water is less than the limit value.

The invention claimed is: 
     
         1 . Method for continuous cleaning of process water circulating in a device for processing waste paper ( 100 ) and/or in a paper machine ( 200 ) of a machine for manufacturing paper from waste paper, in which process water to be cleaned is supplied, from at least one unit of the device ( 100 ) and/or the paper machine ( 200 ), to a process water processing unit having an anaerobic reactor ( 125   a ,  125   b ,  225 ) comprising one or more gas separators ( 504 ), the process water is contacted, in the anaerobic reactor ( 125   a ,  125   b ,  225 ), with anaerobic microorganisms in order to break down impurities contained in the process water, and the cleaned process water is conveyed away from the anaerobic reactor ( 125   a ,  125   b ,  225 ) and returned to at least one unit of the device ( 100 ) and/or the paper machine ( 200 ), wherein at least one unit is selected from one or more of a pulper ( 105 ), sorting device ( 110   a ,  110   b ), dewatering unit ( 115   a ,  115   b ), oxidation/reduction unit ( 112 ), centrifugal sorter ( 202 ), fine sorting device ( 204 ), paper-machine mold part ( 206 ), paper-machine press part ( 208 ), reject treatment unit ( 118   a ,  118   b ,  212 ), fiber recovery unit ( 214 ) and drying part ( 210 ), wherein, in the method, a content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) is measured continuously or discontinuously and, when the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) exceeds a pre-set limit value, process water is continuously supplied, from the anaerobic reactor ( 125   a ,  125   b ,  225 ), to a solid-liquid separator ( 126   a ,  126   b ,  226 ) for separation into a fraction depleted of inorganic solids and a fraction enriched with inorganic solids, wherein the fraction depleted of inorganic solids is returned to the anaerobic reactor ( 125   a ,  125   b ,  225 ) at least in part and the fraction enriched with inorganic solids is conveyed away from the device ( 100 ) and/or the paper machine ( 200 ), until the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) is less than the pre-set limit value. 
     
     
         2 . Method according to  claim 1 , wherein the process water supplied continuously to the solid-liquid separator ( 126   a ,  126   b ,  226 ) from the anaerobic reactor ( 125   a ,  125   b ,  225 ) is removed from the lower region of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         3 . Method according to  claim 1 , wherein the lower region of the anaerobic reactor ( 125   a ,  125   b ,  225 ), viewed in cross section, is designed in a zigzag shape, the zigzag-shaped region extending over 1 to 50% of the height of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         4 . Method according to  claim 1 , wherein the lower region of the anaerobic reactor ( 125   a ,  125   b ,  225 ), viewed in cross section, is designed as a cone ( 514 ), the cone ( 514 ) extending over 1 to 20% of the height of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         5 . Method according to  claim 1 , wherein the limit value for the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) is pre-set to a value between 30 and 45 wt. %. 
     
     
         6 . Method according to  claim 1 , wherein process water from the anaerobic reactor ( 125   a ,  125   b ,  225 ) is supplied continuously to a solid-liquid separator ( 126   a ,  126   b ,  226 ), and the fraction depleted of inorganic solids is returned to the anaerobic reactor ( 125   a ,  125   b ,  225 ), at least in part, until the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) is at least 1% less than the pre-set limit value. 
     
     
         7 . Method according to  claim 1 , wherein the process water is separated in the solid-liquid separator ( 126   a ,  126   b ,  226 ) such that the portion of the fraction depleted of inorganic solids is at least 70 vol. %, and the portion of the fraction enriched with inorganic solids amounts to the remainder up to 100%, with respect to the volume flow of the process water supplied to the solid-liquid separator ( 126   a ,  126   b ,  226 ). 
     
     
         8 . Method according to  claim 1 , wherein the process water is separated in the solid-liquid separator ( 126   a ,  126   b ,  226 ) such that the content of inorganic solids in the fraction enriched with inorganic solids is at least 25% higher than the content of inorganic solids in the fraction depleted of inorganic solids. 
     
     
         9 . Method according to  claim 1 , wherein the solid-liquid separator ( 126   a ,  126   b ,  226 ) comprises one or more centrifugal separators ( 126   a ,  126   b ,  226 ). 
     
     
         10 . Device for processing waste paper ( 100 ), and/or paper machine ( 200 ) of a machine for manufacturing paper from waste paper, the device ( 100 ) and/or the paper machine ( 200 ) comprising a process water processing unit ( 116   a ,  116   b ,  216 ) for cleaning process water circulating in the device ( 100 ) and/or the paper machine ( 200 ), and comprising at least one unit selected from one or more of a pulper ( 105 ), sorting device ( 110   a ,  110   b ), dewatering unit ( 115   a ,  115   b ), oxidation/reduction unit ( 112 ), centrifugal sorter ( 202 ), fine sorting device ( 204 ), paper-machine mold part ( 206 ), paper-machine press part ( 208 ), reject treatment unit ( 118   a ,  118   b ,  212 ), fiber recovery unit ( 214 ) and drying part ( 210 ), and the process water processing unit ( 116   a ,  116   b ,  216 ) comprising:
 i) an anaerobic reactor ( 125   a ,  125   b ,  225 ) comprising one or more gas separators ( 504 ), for anaerobic cleaning of process water, comprising at least one supply line ( 500 ) for supplying process water to be cleaned to the anaerobic reactor ( 125   a ,  125   b ,  225 ), and at least one discharge line ( 512 ) for conveying away cleaned process water out of the reactor ( 125   a ,  125   b ,  225 ), the process water processing unit ( 116   a ,  116   b ,  216 ) being connected to at least one of the at least one unit, such that, during operation of the device ( 100 ) and/or paper machine ( 200 ), process water to be cleaned is supplied from the at least one unit to the process water processing unit ( 116   a ,  116   b ,  216 ) and, therein, the anaerobic reactor ( 125   a ,  125   b ,  225 ), and after the process water processing step cleaned process water is returned into the at least one unit, and   ii) a solid-liquid separator ( 126   a ,  126   b ,  226 ) for separating process water conveyed away from the anaerobic reactor ( 125   a ,  125   b ,  225 ) into a fraction depleted of inorganic solids and a fraction enriched with inorganic solids, comprising a discharge line ( 127   a ,  127   b ,  227 ) for the fraction enriched with inorganic solids and comprising a return line ( 128   a ,  128   b ,  228 ) for returning the fraction depleted of inorganic solids into the anaerobic reactor ( 125   a ,  125   b ,  225 ), at least in part, a further line leading from the anaerobic reactor ( 125   a ,  125   b ,  225 ) to the solid-liquid separator ( 126   a ,  126   b ,  226 ) for supplying process water conveyed away from the anaerobic reactor ( 125   a ,  125   b ,  225 ),   wherein this further comprises iii) a measuring device for measuring the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ), and in that this also comprises a control means which can receive measuring data regarding the content of inorganic solids in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) and into which a limit value and optionally a threshold value can be input, the control means being designed such that it automatically starts the continuous removal of process water from the anaerobic reactor ( 125   a ,  125   b ,  225 ) and the supply thereof into the solid-liquid separator ( 126   a ,  126   b ,  226 ), when an input limit value for the inorganic solids content in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ) is exceeded, and automatically ends the continuous removal of process water from the anaerobic reactor ( 125   a ,  125   b ,  225 ), and the supply thereof into the solid-liquid separator ( 126   a ,  126   b ,  226 ), in the event of falling below the limit value or an input threshold value for the inorganic solids content in the process water contained in the anaerobic reactor ( 125   a ,  125   b ,  225 ).   
     
     
         11 . Device ( 100 ) and/or paper machine ( 200 ) according to  claim 10 , wherein the lower region of the anaerobic reactor ( 125   a ,  125   b ,  225 ), viewed in cross section, is designed in a zigzag shape, the zigzag-shaped region extending over 1 to 50% of the height of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         12 . Device ( 100 ) and/or paper machine ( 200 ) according to  claim 10 , wherein the lower region of the anaerobic reactor ( 125   a ,  125   b ,  225 ), viewed in cross section, is designed as a cone ( 514 ), the cone ( 514 ) extending over 1 to 50% of the height of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         13 . Device ( 100 ) and/or paper machine ( 200 ) according to  claim 10 , wherein the solid-liquid separator ( 126   a ,  126   b ,  226 ) comprises one or more centrifugal separators ( 126   a ,  126   b ,  226 ). 
     
     
         14 . Device ( 100 ) and/or paper machine ( 200 ) according to  claim 10 , wherein the one or more gas separators ( 504 ) in the anaerobic reactor ( 125   a ,  125   b ,  225 ) are arranged at a height of between 30 and 90% with respect to the height of the anaerobic reactor ( 125   a ,  125   b ,  225 ). 
     
     
         15 . Device ( 100 ) and/or paper machine ( 200 ) according to  claim 10 , wherein the one or more gas separators ( 504 ) are designed such that they prevent anaerobic microorganism pellets ( 502 ) from flowing further up in the anaerobic reactor ( 125   a ,  125   b ,  225 ), and thus result in gas adhering to the surface of the anaerobic microorganism pellets ( 502 ) being released and the gas being conveyed away out of the anaerobic reactor ( 125   a ,  125   b ,  225 ) via the gas separator. 
     
     
         16 . Machine for manufacturing paper from waste paper, comprising a device for processing waste paper ( 100 ) and a paper machine ( 200 ) according to  claim 10 , wherein the device ( 100 ) comprises one, two or more stages ( 101   a ,  101   b ), each stage ( 101   a ,  101   b ) comprising a dewatering unit ( 115   a ,  115   b ) and at least one further unit selected from one or more of pulper ( 105 ), sorting device ( 110   a ,  110   b ) and oxidation/reduction unit ( 112 ), each stage ( 101   a ,  101   b ) and the paper machine ( 200 ) in each case comprising a process water processing unit ( 116   a ,  116   b ,  216 ) having the features of  claim 10  relating to the process water processing unit. 
     
     
         17 . Machine according to  claim 16 , wherein the paper machine ( 200 ) comprises at least one unit selected from a centrifugal sorter ( 202 ), fine sorting device ( 204 ), paper-machine mold part ( 206 ), paper-machine press part ( 208 ), reject treatment unit ( 212 ), fiber recovery unit ( 214 ), and drying part ( 210 ).